Let me jump into the fray here and confuse you even more. Actually, maybe I can clarify matters. Is this sentence correct: "A number of us is going downtown to watch the baseball game"?
I would say yes, but most modern grammarians/English teachers would say it’s incorrect. My reasoning is that "a number" is singular, so it must take the singular verb is. They would counter that "a number of us" refers to a collective group and should take the verb are.
Let me settle it by saying you’ll raise fewer eyebrows by using the plural form are, so you should just stick with that (while I continue to use is). However, and here’s where all of us would probably agree, if you said or wrote, "The number of people going to the baseball game is great," that would be correct. The reasoning here is that "the number" refers to a single entity, which is the number, whether it’s 32, 13 or whatever. Therefore it commands a singular verb.
Clear as mud? A number of you are (is) probably still confused.